18 



ARACHXIDA. 



as regards the formation of the brain and the first rudiments of the 

 median eyes. These observers sometimes directly contradict them- 

 selves, or else their accounts are rendered quite incomprehensible by 

 paucity of description or of figures. [See Brauer's recent work.] 



"We must, before leaving this subject, give a brief account of Patten's 

 description of the origin of the brain and eyes, which differs essentially 

 from that given by other authors. Pattex assumes that the cephalic lobes in 

 Scorpio consist of three segments (cf. the structure of the brain in the Insecta). 

 Each of these three segments bears two pairs of eyes, a pair of optic ganglia, 



a. 



Fig. 12.— A, transverse section through the cephalic lobes of Ev.seorpius italicus, showing the 

 two cephalic pits (e), somewhat diagrammatic. B-D, sagittal sections through the cephalic 

 lobes of Biithus carolinianus, showing the formation of the brain and the median eyes. E 

 and F, plans of the cephalic lobes of the same Scorpion at different stages (A, after Laurie, 

 B-F, after Patten), e, cephalic pit ; e,-e„„ the same in the three segments of the cephalic 

 lobes ; g, rudiment of the brain ; g ,-</„„ the same in the three segments ; g.o, optic ganglion 

 (g.o^g.o,,, in the three segments); m.a, median eyes; n.o, optic nerve (n.o„ and n.o,„ in the 

 second and third segments); o.p,-o.p„„ "optic plate" of the three segments ; ;-, retina ; s.a, 

 lateral eyes. 



and a segment of the brain (Fig. 12 E and F). In each segment two regions 

 can be distinguished, a central, cerebral portion and an external optic region, 

 this again being divisible into an inner portion yielding the optic ganglia, and 

 an external region which yields the eyes ("optic plates"). These regions are 

 tli rice repeated from before backward (Fig. 12 E). Whereas other authors 

 observed only the two semicircular depressions of the cephalic lobes, Patten 



